Process for production of unsaturated nitriles



Dec, 23, 1947. I i, 1 WQLK 2,433,182

PROCESS FOR PRODUCTIGN 0F UNSATURATED NITRILES Filed lay 13, 1944 Il`a HOLVNOI .LDVHd rammed um ,f `1.1mmswnur. um a rmi. l lips Petroleum Company, s eorpontlontofneia- @spannen Mumia, serial No. 535,489

sciame. (ci. zoo-4u) The present yinvention relates tothe produc-- 'tion of gacryionitriie (propenenitrile, vinyl cya nidev or cyanoethylene) andA pertains to a new.

and novel process of producing .acrylonitr-ile by,

the pyrolysis ,or thermal reaction of a mixture of hydrogenpcyanide andvinylacetylene ory a cyanobutadiene. l I

Acrylonitrile is a substance of increasing cornmerciai importance, particularly in the synthetic` rubber and-synthetic resin industries. It can be vproduced-by manyniethods. some of which are of interest only from the` standpoint of laboratory preparations andare not adaptable fcically hereinafter, will be 2 skilled inthe art.

In accordance with the process of the present I invention,l vinylacetylene (3-buten-1-yne,

.f CHEC-CH--CHn e or a cyano1,3butadiene `(which occur in two "isomeric iormanarnely,` l

`*hydrogen cyanide is subjected taheating at'a to production of the substance. at low cost.

Several of the more recently 'proposed'methods which appear to have some interest, andat least ,Y one of which is being used in this or a modified.

form, for large-scaleproduction, ofacrylonitrile I at low cost, are the. following:

1. 'Catalytic dehydrogenation at. approximately 700 C. of` propionitrile.(ethyl` cyanide), which may be produced by thereaction of propionic acid and ammonia (see I. G. Farbenindustrie A.G., French Patent 790,262,"and Mitchell and Reid, J. A. C. S., 1931, V01. 53, pages 321 t 330). i

2. Pyrolysis of propionitril'e at approximately 675 C. yields acrylonitrilarbut only a minor proportion of the decomposed propionitriie is acrylonitrile, however. (Rabincvitch and Winkler, Canadian Journal of Research, 1942, vol. 20, part B, pages 69 to 72.)

3. Addition reaction of acetylene and hydrogen cyanide in the presence of an acid-reacting solution of cuprous chloride as a catalystiKurtz application Serial lNo. 343,269, filed June 29, 1940, that is referred to in Kurtz et al., Patents Nos. 2,322,696 and 2,324,854) or solid `barium cyanide or sodium cyanide as catalysts for the reaction of these substances in Vthevapor phase (Baum and Herrman, German Patent No. 559,734).

4. Dehydration of 2-hydroxypropanenitrile (aceialdehyde.` cyanohydrin, alpha-hydroxypropionitrile or lactronitrile) or S-hydroxypropanetemperature within the range of approximately 300toapproximately 800810. (preferably 400 to 650 CJ, preferably in thepresence of catalysts which favor both the addition of lhydrogen cyanide to unsaturated hydrocarbons and cracki ing of nitriies; The proportion of hydrogen cyanide is carefully controlledl as specified here inafter. The .process may be carried out as a batch operation, for example, in an autoclave,

'but is preferably conducted ,as a continuous process in which the mixture of hydrogen cyanide and vinylacetylene or the cyanobutadiene is passed through a tube furnace vand the products are separated from unconverted materials, which are thereafter returned to the reaction zone.

product.

The exact. mechanism by which Vinylacetylene or cyanobutadienes react with hydrogen cyanide to form acrylonitrile has not been determined. Probably not one, but several, reactions occur and acrylonitrile is formed not by a singley reaction but by a combination of several reactions.

Acrylonitrile is obtained in substantial yields in accordance with the process of my invention but it Visfnot the sole substance present in the Substantial proportions of other sub- 4 stances are formed. Suggested reactions, all of nitrilelihydracrylonitrile, ethylene cyanohydrin,

or betahydroxypropionitrile) at approximately 280 Cyin theipresenceof bauxite. 2-hyroxy-` propanenitrilecan be obtained by the reaction f of ethyleneoxide (1,2-fepoxyethane') and hydrogen cyanide (Moureau. Ann. chim.v phys., 1894, series 7, vol. -2,page 145; Erlenmeyer, Annalen, 1878, vol. 191, page 269; U. S. Patent No. 1,891,055 and GermanwPatents Nos. 496,372 and 725,277).

It is an object of the present invention to provide a process for the production of acrylonitrile at low cost.

A further Vobject of the present invention is to provide a process for the production of acrylonitxilel from vinylacetylene or cyano-1,3 butadienes and hydrogen cyanide. e

Further objects and advantages of the invention, some orwhich are, referred' to more spe-v which may and probablydo occur during the course of the `pyrolysis, may be Vrepresented. as

follows:

(l) Vinylacetylene combines with either vone y or twov molecules of hydrogencyanide:

apparent those 5 3 When one, moleculeofhydrogen 'cyanide combines with one molecule of vinylacetylene, the products may be 1-cyano1,3butadiene (A) or 2cyano1,3butadiene (B) or other compounds.

Two molecules of hydrogen cyanide may combine sirable to maintain will be within the range of approximately 1:2 to approximately 1:1, respectively. Thus an excess of vinylacetylene over that oi' vinylacetylene and two molecules of hydrogen cyanide, crack or split to yield two molecules of acrylonitrile. Using 1,4-dicyano-2-butene (C) as typical of these compounds. the reaction may be represented as:

No-cn.c1=cnon,-CN zongen-CN 1,4-dicyano-2-butene Acrylonitrile As hereinbefore indicated, it is not denitely known whether all the foregoing reactions or any of them represent the mechanism by which acrylonitrile is formed in the process of my invention. The product is a rather complex mixture in which acrylonitrile occurs in substantial proportions together with other products, some of which have not been denitely identified.

Vinylacetylene obtained from any source may be used in the process of the present invention.'

It occurs in the C4 hydrocarbon stream resulting from certain thermal cracking and catalytic dehydrogenation processes and may be recovered from other hydrocarbons associated therewith in accordance with the process described in the copending application of Charles K. Buell, Serial No. 513,609, illed December 9, 1943, now Patent No. 2,382,603, patented August 14, 1945, or by other methods.

Cyanobutadienes which can be used in the process of my invention may be obtained by known methods of synthesis. However, they may be conveniently produced by the reaction of vinylacetylene with hydrogen cyanide in the presence of an aqueous solution of cuprous chloride and ammonium chloride, as described in Kurtz et al. Patent No. 2,322,696, in which it is stated that 1cyano1,3butadiene is the product of the reaction of vinylacetylene and hydrogen cyanide.

In practicing the process of my invention,

vinylacetylene and hydrogen cyanide are used in the proportion of at least one molecular proportion of hydrogen cyanide, and preferably two molecular proportions of hydrogen cyanide, for each molecular proportion of vinylacetylene. Greater proportions of hydrogen cyanide may be used and are desirable when reaction conditions are such that polymerization of vinylacetylene or interstoichiometricaly req'uired by the equations hereinabove is maintained.

When using a cyanobutadiene such as l-cyano- 1,3-butadiene as the starting material, only onehalf the amount of hydrogen cyanide which is used with vinyl acetylene is required. The preferred range of molecular ratios of the cyanobatadiene to hydrogen cyanide which it is desirable to maintain in the charge to the pyrolysis in practicing the process of my invention is from approximal-,ely 1:0.5 to approximately 1:1.

Diiuents such as n-butane, and particularly other saturated hydrocarbons, or other substances which are vinert in the reactions and preferably such as are solvents for vinylacetylene and nitriles may, and preferably are. used in the process. These may be charged together with the unsaturated compound to the catalyst reaction zone, or if a batch process is being used, they may be added directly to the reaction mixture or prei.- erably the vinylacetylene or cyanobutadiene is added to the reaction mixture as a solution in the diluent.

The catalysts which are used in the process of my invention iavor the addition of hydrogen cyanide to unsaturated hydrocarbons and cracking or splitting of nitriles. Catalysts which have been specied heretofore for the cracking or splitting of saturated nitriles of higher molecular weight at high pressures and at temperatures from 400 to 800 C. may be used in my process or the process may be conducted without a catalyst but the yields of acrylonitrlle which are obtained are inferior to those obtained with the preferred catalysts specified hereinafter which also favor the addition of hydrogen cyanide. The catalysts which have heretofore been specified for cracking saturated nitriles are aluminum oxide, thorium oxide, osmium oxide, iron oxide, glass, aluminum oxide on charcoal, copper on fused aluminum oxide, and iron on fused aluminum oxide (Ralston et al., J. Amer. Chem. Soc., 1932, vol. 59, page 988 and Patent No. 2,033,536). The preferred catalysts for use in the process of my invention are oxides of alkaline-earth metals such as calcium, strontium, barium and the like, or cyanides of these metals. During the reaction metal oxides, if such are used, are converted to cyanides. Other alkaline-earth metal compounds which decompose to oxides or cyanides in the reaction may also be used as initial catalytic materials. These alkaline-earth metal oxides or cyanides, which are relatively refractory substances, may be replaced partially or used in admixture with other metal oxides and cyanides or metal compounds which decompose to such oxides or cyanides, such as, for example, those of copper, iron, cobalt, nickel, thorium, osmium. etc. 'I'he active catalytic materials may be used in conjunctionV or admixture with heretofore known cracking or splitting materials such as aluminum oxide, bauxite, glass, etc. Preferably the alkaline-earth metal oxide or cyanide is supported or deposited on a carrier material, which may be charcoal, but which preferably is aluminum oxide or other material that has a cracking or splitting action point of pure acrylonitrile is 'Z8-9 C.).

support. t t t Examples oftypical preferred catalytic compositions suitableftor use in the process of my invention are:

(l) Barium cyanide supported on porous alundum granules. t

(2) Calcium cyanide supported on active charcoal. I

(3) Barium cyanide and copper cyanide in equal parts by weight deposited on silica granules.

The catalytic" materialfmay be incorporated with the carrier or'support material in conventional manners." Thus, the two materials may be con-:mingled by mixing of the dried materials.

Alternatively, the catalytic carrier material may be impregnated with a solution or a suspension of the alkaline-earth cyanide and thereafter dried: for example, by passing a stream of heatedl nitrogen gas thereover, or, if oxides are to be the initial catalytic materials, they may be incorporated on the support in manners that are conventional in the deposition of metal oxides on catalyst supports. v

The temperatures at which the process of my invention is"conducted are generally within the range of approximately 300 to approximately 800 C.. with the most desirable and preferred portion of this range being approximately within the limits of 400 to 650 C. The pressures may be within the range of approximately atmospheric to superatmospheric pressures of approximately 1000 pounds per square inch. In continuand which is ln a form suitable for use as catalyst ous processes, the pressure is preferably atmospheric or slightly above this, namely, upto approximately 50 pounds per square inch gage.

In conducting the process in a continuous manner, by passing a mixture of vinylacetylene and hydrogen cyanide over the catalyst at an elevated temperature, the contact period should be relatively short. Thus, for example, the flow of feed to the catalyst reaction zone should generally be maintained at a ratewithin the range equivalent to approximately 0.2 to approximately 5 liquid volumes per volume of catalyst per hour, although these limits may be varied somewhat dependent upon the proportion of diluent present, the temperature and pressure of operation, the nature of the catalyst, and the molecu lar ratio of the reactants.

Examples of preferred methods of practicing the process of my invention are as follows:

Example 1 Into an autoclave of approximately 500 cc. capacity are placed 50 grams of a solution of vinylacetylene in n-butane containing 75% by weight of n-butane. To the autoclave is then added 5 grams of al catalyst comprising barium cyanide deposited on a porous alundum carrier. Approximately 13.5 grams (2 molecular proportions based on the vinylacetylene present) of liquid hydrogen cyanide are then added to the autoclave and the autoclave is sealed. The autoclave is then heated while it is agitated and without release of pressure to approximately 500C. and maintained at this temperature for approximately 30 minutes. It is then allowed to cool and acrylonitrile is recovered from the products in conventional manner.

The product may be recovered by separating by fractional distillation a fraction having a boiling range of approximately '70 to 80 C. (boiling This 6 fraction may then be trashed withaqueous sodium hydroxide solution, dried overcalcium chlof ride `and redistliled. A substantial yield of acryl` onitril'eisobtained. 1

` Example 2 The process described in 'Example 1 is repeated but a purified 1cyano1,3butadiene dissolved in n-pentane is used instead of vinylacetylene together with a smaller proportion ofhydrogen cyanide. The charge to the autoclave comprises I9 grams of a 25% by weight solution of l-cyano- 1,3-butadiene dissolved in n-pentane and approximately 6 grams of hydrogen cyanide. These quantities correspond approximately to an equimolecular ratio of reactants.

The yield of acrylonitrile which was obtained, expressed as per cent of the theoretical yield, was slightlygreater than that obtained in Example 1.

Eatarrip'le:k 3

. molecular ratio of vinylacetylene to hydrogen cyanide is approximately 1:2 and that the llow rate of the mixed stream, which is passed through heater 9, line I0, and over the catalyst in catalyst case II, yls approximately 0.5 liquid volumes of mixture per volume of catalyst per hour. The mixed stream which enters heater 9 is heated therein to a temperature of approximately 500 C. and enters the catalyst case I I through line I0.

A catalyst comprising barium cyanide supported on an alundum carrier is disposed in the catalyst case.

After leaving the catalyst case II through line I2, the eiiluent product stream is cooled in cooler I3v to a temperature of approximately 50 C. or lower and is passed to fractionator I4 through line I5.

In fractionator I 4 a separation is made between urireacted vinylacetylene (boiling point, approximately 5 C.) and unreacted hydrogen cyanide (boiling point, approximately 26 C.) and higher-boiling products. The vinylacetylene is passed as overhead from fractionator Il through line I6 to vinylacetylene storage 5. The bottoms from fractionator ll-are passed through line Il to fractionator I8, in which unreacted hydrogen cyanide is recovered as overhead and is conducted through line I9 to storage tank I. The bottoms from fractionator I8, which comprise the acrylonitrile, are passed through line 20 to washer 2 I. In washer 2l the bottoms 'are subjected to washing with an aqueous solution of sodium hydroxide and are passed through line 22 to fractionator 23. Prior to entering fractionator 23 the material may be and preferably is dried by agitation with calcium chloride or other suitable desiccant.

Separation of acrylonitrile from other substances is eiected in fractionator 2l. The acrylonitrile fraction (boiling point of pure acrylonitrile is '7s-9 C.) is passed to storage via line 24 and the higher-boiling products, which inanais:

, particularly to the reaction of vinylacetylene and cyanobutadienes to produce acrylonitrile'it will be apparent that the process of the invention is adaptable to the reaction of homologues of these materials to produce homologous unsaturated nitriles.

Inasmuch as the foregoing speciilcation comprises preferred embodiments of the invention, it is to be understood that the invention is not limited thereto and that modifications and variations may be made therein to adapt the process of the invention to particular uses without departing substantially from its scope or the scope of the appended claims.

I claimt 1. A process for the production of acrylcnitrile which comprises subjecting a compound selected from the group consisting of vinylacetylene and cyanobutadienes to cracking at a temperature within the range of about 400 C. to about 650 C. in the presence of hydrogen cyanide and an alkaline earth metal cyanide catalyst promoting the addition of hydrogen cyanide to unsaturated hydrocarbons, said hydrogen cyanide being present in substantial proportion but not in excess of that I amount required to convert all of the said substance to acrylonitrile. f

2. A process according to claim 1 wherein the alkaline earth metal cyanide catalyst is supported on a metal oxide cracking catalyst.

3. A process for the production of acrylonitrile which comprises cracking vinylacetylene in the presence of hydrogen cyanide in a molecular proportion within the range of approximately one molecular proportion of vinylacetylene to from approximately one to approximately two molecular proportions of hydrogen cyanide, in the presence of a catalyst comprising an alkaline earth metal cyanide supported on a cracking catalyst, at a temperature within the range of approximately 400 C. to approximately 650 C.

4. A process for the production of acrylonitrile which comprises heating together under pressure and at a temperature of approximately 500 C. and in the presence of a catalyst comprising barium cyanide deposited on a porous alundum carrier a mixture of approximately 1 molecular 8., proportion of vinylacetylene dissolved in a saturated hydrocarbon diluent and approximately 2 molecular proportions of hydrogen cyanide.

5. A continuous process for the production of acrylonitrile which comprises passing a'mixture of vinylacetylene and hydrogen cyanide in the vapor-phase and in the molecular ratio of approximately 1:2 and at a temperature of approximately 500 C. into contact with a catalyst comprising barium'cyanide supported on an alundum carrier, recovering unreacted vinylacetylene and unreacted hydrogen cyanide from the eiiluent product, recirculating said recovered vinylacetylene and hydrogen cyanide to the catalyst, and recovering acrylonitrile from the eluent product.

6. A process accordingto claim 1 wherein the alkaline earth metalcyanide is supported on an aluminum oxide carrier.

7. A process for the production of acrylonitrile which comprises heating together under pressure and at a temperature in the range from 400 C. to 650 C. a mixture of approximately one molecular proportion of vinylacetylene dissolved in a saturated hydrocarbon diluent and approximately two molecular proportions of hydrogen cyanide in the presence of a catalyst comprising a cyanide of an alkaline earth metal supported on an alundum carrier.

8. A continuous process for lthe production of acrylonitrile which comprises passing a mixture of vinylacetylene and hydrogen cyanide in the molecular ratio of approximately 1:2 at a temperature in the range from 400 C. to 650 C. into contact with a catalyst comprising a cyanide of an alkaline earth metal supported on an alundum carrier, recovering unreacted vinylacetylene and unreacted hydrogen cyanide from the effluent product, recirculating said recovered vinylacetylene and hydrogen cyanide to the catalyst, and recovering acrylonitrile from the effluent product.

. I. LOUIS WOLK.

REFERENCES CITED The following references are of record inthe le of this patent:

UNITED STATES PATENTS 

